This invention relates to special effects video devices such as character generators used in television studios and broadcast facilities to generate video signals that represent alpha numeric characters and other symbols to be presented in a television display. More specifically, the invention relates to systems for generating video signals that are jagged-edge anti-aliased. Jagged edged symbol boundaries caused by sharp transitions between adjacent elements of a video display raster can be eliminated or anti-aliased by providing the portions of the video data or color signal that correspond to discrete raster display locations that are crossed by symbol boundaries with color values that are mixtures of the colors on opposite sides of that boundary. But, a very large amount of data must be processed at a very high rate to provide and maintain anti-aliasing, particularly during symbol movement or animation.
The popular design approach for a wide range of character generators utilizes frame buffers to manipulate symbols or update video signals. Frame buffer systems achieve animation by moving blocks of data representing portions of a video image to be modified, formulating vectors, and filling memory blocks of the frame buffers with desired display patterns. They require complex electronics to identify the portion of a display to be modified and manipulate blocks within a frame buffer representing those portions of the image. Approximately 33 nanoseconds (ns) are available and required to update a complete non-moving image in real time video. If significant motion of symbols (that is, text, characters, logos and other objects) occurs, the time for recalculation of an entire frame exceeds the 33 ns period. To achieve motion a compromise must be made, which usually involves dropping some or all anti-aliasing.
There have been prior efforts to design a pipeline system that would regenerate a complete video signal representing all portions of an image each field or frame and thereby avoid the requirement of frame buffer systems to identify particular portions of a video signal or blocks of data to be modified from one field to the next. The prior effects have included use of symbol boundaries to reduce the amount of data from that which must be processed in a frame buffer system. They have not sufficiently reduced the number of calculations or amount of data that must be processed to maintain anti-aliasing, or sufficiently increased the speed of the required calculations to provide a practical successful system. The capability of both frame buffer and prior pipeline designs has been limited with respect to dynamic display characteristics, the processing speed and amount of data required to be handled for anti-aliasing and the interrelationship between anti-aliasing, and the other capabilities of the system.